1. Field of the Invention
The present invention relates to a fixed pattern noise removal method, and more particularly, to a fixed pattern noise removal method in an image sensor which only needs to calculate each compensation value corresponding to each pixel column for compensation, so as to save memory usage and reduce computation complexity.
2. Description of the Prior Art
Generally for an image sensor, the pixels used for image sensing are not uniform in dimension, spacing, and efficiency. Also, a row sampler such as the correlation double sampling (CDS) sampling active pixel values row by row may result in deviations. That is, a specific sampler is used for a specific column pixel, and thus if samplers in a row are not uniformly designed or fabricated, sampled pixel values of pixel columns may have deviation, which causes noise in vertical lines of the image due to the sampling non-uniformity. Thus, the image captured by the image sensor may have a non-random fixed pattern noise (FPN) induced by the drawback of the hardware architecture.
For example, please refer to FIG. 1A and FIG. 1B, which illustrate schematic diagrams of a real image IMG and a noise image NIMG with a column fixed pattern noise, respectively. As shown in FIG. 1A and FIG. 1B, since the specific sampler is used for a specific column pixel, and samplers in a row are not uniformly designed and fabricated, the sampled pixel values of the pixel columns have fixed pattern noises in vertical lines of the image (the vertical stripes as shown in FIG. 1B) due to the sampler non-uniformity.
In such a situation, a conventional technology takes a real picture and an optical black picture separately under the same condition, and then subtracts the optical black picture from the real picture to remove the fixed pattern noise. However, this method requires the image sensor to record and store the whole optical black picture for different parameter control (e.g., temperature, gain value, exposure time), which consumes a huge memory. Thus, there is a need for improvement of the prior art.